This invention relates to ventilators for the space below the roof of a building and, in particular, relates to roof ridge ventilators for exhausting air from the attic of a house.
Roof ridge ventilators are installed overlying the open ridge of and along the length of a building for exhausting heated air from the space below the roof of the building. These ventilators are installed in cooperation with ventilators at the soffits of the building roof to provide a ventilation system in which air is exhausted from the space below the roof through the roof ridge ventilator and is replenished through the soffit ventilators. An example of such a ventilator system is disclosed in U.S. Pat. No. 3,036,508.
Ventilation of the attic of a building has become increasingly important to remove the gaseous water vapor which migrates into the attic from the living quarters of the building. This migrated water vapor when condensed into liquid water in a cold attic above the living quarters can reduce the rating of installation installed in the attic and can have deleterious effects on the structure of the roof if not removed. Ventilation of the attic thus is important to remove this airborne water vapor from the attic.
In an optimum roof ridge soffit ventilator system, there is a balance between the net free open area presented by both the roof ridge and soffit ventilators. The phase "net free open area of a ventilator" is intended to mean the cross sectional area of a ventilator which is open for passage of air therethrough. A balance between the net free open area of a roof ridge and soffit ventilator is difficult to obtain. In many new homes there is a lack of sufficient soffit area in which to provide the soffit ventilators. Most existing homes do not have sufficient soffit ventilation to provide the balanced system. Remodeling contractors and home owners are unwilling to install soffit ventilators and in many cases, it is difficult to do so. In many instances, fire codes prevent the installation of soffit vents within three feet of doors and windows. Further, in homes such as those having cathedral ceilings, the insulation in the space below the roof would prevent the clear passage of air from the soffit ventilators to the roof ridge ventilator even if soffit ventilators were installed. Thus, in many new and existing homes there is an occurrence of an out of balance roof ridge/soffit ventilator system.
These out of balance ventilation systems are subject to several problems, one of which is the infiltration of moisture through the ventilators. An out of balance system favoring the soffit vents will produce a weak ventilation system but little harm will occur from infiltration of moisture through the roof ridge or soffit ventilators into the space below the roof of the building. In an out of balance system favouring the roof ridge ventilators, however, a phemonenon occurs in response to normal winter winds that will infiltrate moisture such as snow through the roof ridge ventilator.
This phenomenon occurs when the wind currents are from a direction which is parallel to or at a small angle to the length of the roof ridge ventilator. This phenomenon provides low pressure areas along a windward portion of the roof ridge ventilator as a result of the wind striking the structure of the building below the roof and being deflected over the roof. These low pressure areas serve to exhaust air through the windward portion of the roof ridge ventilator from the space below the roof. Because of the unbalance of the ventilator system favoring the roof ridge ventilator, the air which is exhausted through the windward portion of the roof ridge ventilator is replenished by air being admitted in through the roof ridge ventilator and not the soffit ventilators. This admission of air occurs along a leeward portion of the roof ridge ventilator which is subject to high pressures as the deflected wind again approaches the roof. In winter months, this phenomenon will infiltrate moisture in the form of snow through the roof ridge ventilator and into the attic of the building. This snow subsequently will melt which causes damage to the structure of the building and additionally wets any insulation and reduces the insulation rating thereof.
Further, a roof ridge ventilator will infiltrate moisture such as snow with winds occurring at other angles when a roof ridge ventilator is installed on a roof having a pitch greater than 8/12 without the use of a shim commonly known as a cant strip between the ventilator and the building roof.
The invention prevents the infiltration of moisture such as snow through a ridge ventilator by providing a high impedence to such moisture while presenting a low impedence for the air passing through the ridge ventilator.
It is known to provide a wire screen in a roof ridge ventilator to prevent the passage throughthrough of birds, insects or foreign manner. See U.S. Pat. No. 3,036,508, for example. There, a wire screen mesh is held over the free open areas of the ventilator by baffles which additionally act as splash guards. The screen has a thickness substantially the thickness of the wire forming the screen and presents what may be referred to as a single plane of openings for the air to pass through. As each opening between the wires becomes clogged by moisture such as snow or frost, the net free open area of the ventilator is reduced proportionately. Additionally, any moisture which passes through the plane of the screen is free to pass through to the space below the roof.
The invention provides a filter medium which is installed in the ventilator over the ventilator openings and which has a substantial thickness. The filter medium traps or blocks the passage of moisture such as snow passing through the openings. The ventilator openings thus may be much larger than the size of the snow particles which means that the openings will not easily become clogged by the snow and that the amount of the net free open area of the ventilator remains stable. The filter medium will filter the snow particles through out the thickness of the filter medium. Thus the snow particles have to travel a relatively long distance through the filter medium compared with the single plane of the wire screen before the snow particles are free to pass to the space below the building roof. Additionally, the snow particles trapped in the filter medium will not proportionally reduce the net free area of the ventilator. The air passing through the filter medium may move laterally through the filter medium and around filtered snow or other moisture and out of the ventilator to ambient atmosphere or to the attic space below the roof of the building
It is known to use filter media to trap airborne particulate matter in ventilators, for example see U.S. Pat. Nos. 2,171,400; 3,657,991 and 4,048,911. But every one of these references discloses the use of a filter medium in what may be called an active ventilator system where there is a motor driven fan for forcing the air through the ventilator. The roof ridge ventilator of the invention is distinguishable from these systems by the lack of the motor driven fan, such a roof ridge ventilator being what may be called a passive ventilator. Moreover, the filter media used in these active systems are intended to remove dirt and dust and are not intended to remove or prevent the infiltration of moisture such as snow or rain through a ventilator.